A plastic optical waveguide made of a thermoplastic polymer with no rubber elasticity such as polymethyl methacrylate is known and practically used. However, any optical waveguide made of an elastomer with rubber elasticity has not been practically used since it has very large attenuation of light transmission due to roughness of the core surface caused during the production of the optical fiber.
One of the methods for producing an elastomeric optical fiber comprises pouring a liquid polymer for forming the core in a hollow member such as a tube which may be used as a cladding, cross-linking the polymer by, for example, heating and releasing the cross-linked core from the hollow member to obtain a core when the member is not used as the cladding. In this method, the roughness of the inner surface of the hollow member is transferred onto the surface of the released core. When the hollow member as such is used as the cladding, irregularities such as peeling at an interface between the core and the cladding are formed since the liquid polymer shrinks during cross-linking. The surface roughness or the irregularities of the interface result in increase of attenuation of light transmission. In addition, since the liquid polymer should be poured in the hollow member by this method, the optical fiber cannot be longer than about 10 m.